This application claims priority to prior application JP 2002-83598, the disclosure of which is incorporated herein by reference.
The present invention relates to a piston unit, which is installed in a piston compressor, and in particular, to such a piston unit with a reduced weight.
Generally speaking, a piston unit comprises a piston and a piston rod connected to the piston. The piston rod is also called a connecting element and is for connecting the piston with an external drive or driven object. The piston comprises a piston head comprising a compression surface and a piston skit, portion. The piston skirt portion is connected to the piston head and serves to guide the piston without inclination in a cylinder.
There is a need for a light-weight piston unit for use in a piston compressor. To meet the need, various types of pistons unit are developed. For example, JP-A 10-299655 or 2000-274350 discloses a piston unit where the piston skirt portion is partially cut away to form side opens axially extending from the rear end. In the structure, the skirt portion is low in rigidity and mechanical strength. Accordingly, the wall thickness of the skirt portion is required large, which results in the insufficient reduction of weight of the piston unit.
It is an object of the present invention to provide a piston unit which is reduced in weight without substantial degradation of mechanical strength of the piston skirt portion.
This invention is directed to a piston unit comprising a piston, which has a compression end surface, and a connecting element, which is fixed to the piston and extends therefrom opposite to the compression end surface. The piston has a piston outer diameter. According to the invention, the piston comprises:
a first ring having an outer diameter equal to the piston outer diameter and having a first axial end and a second axial end opposite to the first axial end;
a second ring having an outer diameter equal to the piston outer diameter and having a third axial end and a fourth axial end;
joint member jointing the first and the second rings to each other between the second axial end of the first ring and the third axial end of the second ring at angularly-spaced positions, so that the first and second rings are disposed on the same center axis and apart from each other in the axial direction, and
a circular disk member fixedly mounted in and closing the first axial end of the first ring, and having an exposed surface, as a compression end surface, out of the first ring.
The connecting element is fixed to the fourth axial end of the second ring at angularly-spaced positions.
In the piston unit according to this invention a piston head comprises the circular disk member, and the skirt portion comprises the first ring and the second ring jointed by the joint members at angularly-spaced positions. The piston has angularly-spaced windows in the skirt portion and is, therefore, reduced in the weight.
The skirt portion is supported by connecting member connected to the second ring at angularly-spaced positions. Therefore, the skirt portion is not degraded by presence of the windows.
Further objects, features and advantages of the present invention will be understood from the following description of embodiments of the invention in connection with figures.